With respect to the trend in demand of petroleum products, the demand of middle fractions such as kerosine, diesel fuel, light residual fuel oil, etc., has increased, and, on the other hand, the demand of heavy oils such as heavier residual fuel oil, etc., has remarkably decreased. This trend is supposed to continue for a long time. Since the petroleum products are those obtained in series and amounts of each fraction depend upon the kind of crude petroleum, it is difficult to control production of each product so as to agree with the demand. On the other hand, in view of the supply of the crude petroleum, the ratio of heavy crude petroleum to the whole crude petroleum has a tendency to increase year by year. Considering such a demand structure, namely, an increase of heavy crude petroleum and deficiency of middle fractions, it has been desired to establish a hydrocracking technique for producing middle fractions having good quality from residual oil in a high selectivity. Further, because hydrogen treated residual oil produced by removing light fractions from a hydrocracking product is used mainly as fuel, it is necessary that sulfur compounds are removed from it. In this case, it is of course necessary to have a long period of continuous operation (catalyst life). Accordingly, it has been greatly desired to develop a hydrogen treating catalyst having long catalyst life by which hydrocracking and hydrodesulfurization of heavy mineral oil occur at the same time.
Hitherto, catalysts which cause hydrodesulfurization, hydrodemetallization or hydrocracking of heavy oil such as residual oil have been known. Catalysts showing such function which have a specific pore size distribution have been described in Japanese Patent Publication Nos. 38142/70, 38143/70 (corresponding to U.S. Pat. No. 3,383,301), 20911/71, 44001/72, 33321/74 (corresponding to U.S. Pat. No. 3,766,057), 41641/76 (corresponding to U.S. Pat. No. 3,843,509), 10942/79, 37163/79, 95/80, 44795/80, 44796/80 (corresponding to U.S. Pat. No. 3,730,879), 52620/81 and 31457/82 and Japanese Patent Application (OPI) No. 27036/80 (the term "OPI" as used herein refers to a "published unexamined Japnese patent application open to public inspection"). However, catalysts described in the above described Japanese Patent Publication Nos. 38142/70, 38143/70, 20911/71, 41641/76, 44795/80 and 44796/80 have a fault in that the catalyst life is reduced when carrying out hydrodesulfurization and hydrocracking at the same time. The reason for this is believed to be that the catalysts have a small total pore volume and an unsuitable pore size distribution. Catalysts described in Japanese Patent Publication Nos. 33321/74, 10942/79 and 52620/81 and Japanese Patent Application (OPI) No. 27036/80 also have a fault in that the catalyst life is reduced when carrying out hydrodesulfurization and hydrocracking at the same time. The reason for this is believed to be that the catalysts have an unsuitable pore size distribution. Catalysts described in Japanese Patent Publication Nos. 37163/79 and 31457/82 have a fault with respect to the catalyst life, because those having a suitable pore volume are not suitable in the pore size distribution and those having a suitable pore size distribution are not suitable in the pore volume. Catalysts described in the above described Japanese Patent Publication Nos. 38143/70, 44001/72, 33321/74, 10942/79, 95/80, 44795/80, 44796/80, 52620/81 and 31457/82 and Japanese Patent Application (OPI) No. 27036/80 are essentially catalysts for hydrodesulfurization, and the catalyst life becomes short, if hydrocracking is carried out at the same time as hydrodesulfurization. Catalysts described in, for example, examples in Japanese Patent Publication Nos. 33321/74, 44795/80 and 31457/82 do not contain nickel as a hydrogenating metal component and are not suitable for carrying out hydrodesulfurization and hydrocracking at the same time. Catalysts described in Japanese Patent Publication No. 37163/79 are catalysts for hydrodemetallization, and the catalyst life becomes short when hydrodesulfurization and hydrocracking are carried out at the same time.
Namely, hitherto, catalysts for desulfurization, catalysts for demetallization and catalysts fcr hydrocracking have been used, respectively, as hydrogen treating catalysts. As the catalysts for desulfurization and the catalysts for demetallization, alumina base-containing catalysts are mainly used. As the catalysts for hydrocracking, crystalline or amorphous silica-alumina base-containing catalysts have been generally used or studied, because strong acidity is required as compared with the catalysts for desulfurization and the catalysts for demetallization. However, these prior hydrogen treating catalysts have faults in that the hydrocracking activity is insufficient, the hydrodesulfurization activity is insufficient or the catalyst life is insufficient, because these prior catalysts have substantially a single function, i.e., any one of hydrocracking, hydrodesulfurization, or hydrodemetallization function. In other words, the prior catalysts for desulfurization have been developed concentrating on only desulfurization activity and designed so as to have a high desulfurization activity at a comparatively low temperature, and, consequently, they exhibit a low cracking rate for heavy mineral oil. Further, in the case that these catalysts are allowed to react at a temperature range at which the cracking rate becomes high, namely, at a high temperature range capable of causing hydrocracking at an acid site of alumina, desulfurization activity rapidly reduces by rapid deposition of metal, coke, etc., to shorten the catalyst life. Accordingly, they are not suitable for the reaction process for such a purpose.
On the other hand, with respect to reaction temperature, there are problems of generation of sludge in the reaction products, congelation of the catalyst particles, limitation of reaction temperature in designing the apparatus, and the like, and it is impossible to increase the reaction temperature without any restriction. Further, the silica-alumina base-containing catalysts have a fault of having low desulfurization activity. Therefore, in the case of carrying out hydrocracking heavy oil having a high sulfur content, it is necessary to carry out two stage processing wherein desulfurization reaction is conducted in the first step and, thereafter, hydrocracking reaction is conducted in the second step.